A scale-resistant cross-linked polymer fracturing fluid and its preparation method

Abstract

The present invention discloses an anti-scaling cross-linked polymer fracturing fluid and a preparation method thereof, and relates to the technical field of petroleum fracturing fluid. When preparing the anti-scaling cross-linked polymer fracturing fluid, the present invention first reacts allylamine hydrochloride with epichlorohydrin to obtain a double-bond chlorinated intermediate; the double-bond chlorinated intermediate is reacted with lauryl amide propyl dimethylamine to obtain a cationic monomer; the cationic monomer is copolymerized with acrylamide to obtain a cationic polymer; L-lysine is reacted with formaldehyde and phosphorous acid to obtain phosphoric acid-modified lysine; phosphoric acid-modified lysine is reacted with allyl glycidyl ether to obtain a phosphoric acid-modified monomer; acrylamide is copolymerized with an anionic monomer to obtain an anionic polymer; the anionic polymer and the cationic polymer are dissolved in water to prepare the anti-scaling cross-linked polymer fracturing fluid. The anti-scaling cross-linked polymer fracturing fluid prepared by the present invention has the advantages of anti-scaling, good temperature resistance, good shear resistance, and self-crosslinking.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum fracturing fluids, in particular to an anti-scaling cross-linked polymer fracturing fluid and a preparation method thereof. Background Art

[0002] Scale is a type of deposit formed by the long chemical reaction between high concentrations of alkaline earth metals in shale reservoirs and anions in the water, which accumulates in pipes and rock formations. These deposits can remain in the wellbore, casing, production tubing, downhole completion equipment, and pipelines of oil wells. Due to various factors, they can form aggregates, causing pipeline blockages, increased friction, and impeded fluid flow, leading to problems such as reduced well productivity, pump sticking, and difficulty filling injection wells. However, this phenomenon is common in many areas near oil production, and scale forms throughout the entire process from oil and water injection equipment to the reservoir and then to surface equipment. Oil well scaling refers to the accumulation of deposits within the injection and production system, piping, and processing systems of oil wells. Existing anti-scaling measures rely on injecting a single scale inhibitor to prevent the accumulation of scale deposits in the wellbore, or even on-site compounding of a single scale inhibitor with fracturing fluid to enhance its performance. However, these simple methods result in suboptimal scale inhibition and removal, increasing the difficulty of fracturing operations, reducing efficiency, and leading to uncontrollable factors during operation. To address this issue, a scale inhibitor monomer is introduced into the synthesis process, and a highly effective scale-inhibiting fracturing fluid thickener is synthesized in one go through aqueous solution polymerization, achieving the goal of integrated fracturing and scale inhibition. Summary of the Invention

[0003] The object of the present invention is to provide an anti-scaling cross-linked polymer fracturing fluid and a preparation method thereof, so as to solve the problems existing in the prior art.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] An anti-scaling cross-linked polymer fracturing fluid, wherein the anti-scaling cross-linked polymer fracturing fluid is prepared by dissolving an anionic polymer and a cationic polymer in water;

[0006] The cationic polymer is prepared by copolymerizing a cationic monomer and acrylamide via a composite initiator;

[0007] The cationic monomer is prepared by reacting a double-bond chlorinated intermediate with lauryl amide propyl dimethylamine;

[0008] The double bond chlorinated intermediate is prepared by reacting allylamine hydrochloride with epichlorohydrin;

[0009] The anionic polymer is prepared by copolymerizing acrylamide and anionic monomers via a composite initiator;

[0010] The anionic monomer is a mixture of phosphoric acid-modified monomer, maleic anhydride, and 2-acrylamido-2-methylpropanesulfonic acid;

[0011] The phosphoric acid-modified monomer is prepared by reacting phosphoric acid-modified lysine with allyl glycidyl ether;

[0012] The phosphoric acid-modified lysine is prepared by reacting L-lysine with formaldehyde and phosphorous acid.

[0013] As an optimization, the composite initiator is a mixture of ammonium persulfate, ascorbic acid, azobisisobutyramidine hydrochloride, and azobisisobutyronitrile.

[0014] A method for preparing a scale-resistant cross-linked polymer fracturing fluid comprises the following steps:

[0015] (1) Allylamine hydrochloride, triethylamine, and methanol were mixed, and epichlorohydrin was added dropwise in an ice-water bath. The mixture was reacted, filtered, and rotary evaporated to obtain a double-bond chlorinated intermediate.

[0016] (2) Mixing the double-bond chlorinated intermediate, lauryl amide propyl dimethylamine, and anhydrous ethanol, reflux reaction, rotary evaporation, washing, suction filtration, and rotary evaporation to obtain a cationic monomer;

[0017] (3) acrylamide, cationic monomer, pure water, and anti-crosslinking agent are mixed, and a composite initiator prepared by uniformly mixing ammonium persulfate, ascorbic acid, azobisisobutylamidine hydrochloride, and azobisisobutylonitrile is added under a nitrogen atmosphere, and the mixture is reacted, cooled, washed, filtered, dried, crushed, and granulated to obtain a cationic polymer;

[0018] (4) L-lysine, formaldehyde aqueous solution, and phosphorous acid are mixed, refluxed, and dried to obtain phosphoric acid-modified lysine;

[0019] (5) Phosphoric acid-modified lysine, allyl glycidyl ether, and hexadecyltrimethylammonium bromide are mixed, stirred, heated for reaction, washed, and dried to obtain a phosphoric acid-modified monomer;

[0020] (6) acrylamide, phosphoric acid-modified monomer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, and pure water are mixed, cooled under a nitrogen atmosphere, and a composite initiator prepared by uniformly mixing ammonium persulfate, ascorbic acid, azobisisobutylamidine hydrochloride, and azobisisobutylonitrile is added, reacted, cooled, taken out, cut into pieces, dried, crushed, and granulated to obtain an anionic polymer;

[0021] (7) By weight, 5-6 parts of cationic polymer, 2-3 parts of anionic polymer, and 1000 parts of pure water were mixed evenly, and stirred at 200-300 r / min for 30-40 min at room temperature to prepare an anti-scaling cross-linked polymer fracturing fluid.

[0022] As an optimization, the double-bond chlorinated intermediate in step (1) is prepared by uniformly mixing 4-5 parts of allylamine hydrochloride, 4.76-5.95 parts of triethylamine, and 40-50 parts of methanol in parts by mass, and then adding 8.9-11.13 parts of epichlorohydrin dropwise in an ice-water bath within 1 hour. After the addition is completed, the mixture is reacted at 25-30°C and 300-400 r / min for 14-15 hours, filtered, and the filtrate is rotary evaporated to remove the solvent.

[0023] As an optimization, the reaction process of the double-bond chlorinated intermediate in step (1) is as follows:

[0024] .

[0025] As an optimization, the cationic monomer in step (2) is calculated by weight, and 4 to 5 parts of double-bond chlorinated intermediate, 11.75 to 14.69 parts of lauryl amide propyl dimethylamine, and 15 to 20 parts of anhydrous ethanol are mixed evenly, refluxed at 80 to 85° C. for 22 to 24 hours, and the solvent is removed by rotary evaporation. The product is washed 3 to 4 times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate is rotary evaporated to obtain the product.

[0026] As an optimization, the reaction process of the cationic monomer in step (2) is as follows:

[0027] .

[0028] As an optimization, the cationic polymer in step (3) is prepared by uniformly mixing 5-6 parts of acrylamide, 6.34-7.61 parts of cationic monomer, 30-35 parts of pure water and 0.3-0.4 parts of anti-crosslinking agent in parts by mass, adding a composite initiator prepared by uniformly mixing 0.025-0.03 parts of ammonium persulfate, 0.01-0.011 parts of ascorbic acid, 0.005-0.006 parts of azobisisobutylamidine hydrochloride and 0.025-0.03 parts of azobisisobutylonitrile under a nitrogen atmosphere at 45-50°C and 400-500 r / min, reacting for 2 hours, cooling to room temperature, washing with anhydrous ethanol 2-3 times, filtering, and drying the solid in a vacuum at 60-70°C for 5-6 hours, crushing and granulating to obtain the product.

[0029] As an optimization, the anti-crosslinking agent in step (3) is one of sodium formate and urea.

[0030] As an optimization, the phosphoric acid-modified lysine in step (4) is prepared by uniformly mixing 6-7 parts of L-lysine, 20-24 parts of 40 wt% formaldehyde aqueous solution, and 13.46-15.71 parts of phosphorous acid, by weight, and reacting under reflux at 105-110°C for 2.5-3 h, and drying at 50-60°C for 10-12 h.

[0031] As an optimization, the reaction process of the phosphoric acid-modified lysine in step (4) is as follows:

[0032] .

[0033] As an optimization, the phosphoric acid-modified monomer in step (5) is prepared by uniformly mixing 5-6 parts of phosphoric acid-modified lysine, 1.09-1.31 parts of allyl glycidyl ether, and 0.006-0.007 parts of hexadecyltrimethylammonium bromide, calculated by mass, and first stirring at 60-65°C and 300-400 r / min for 20-30 min, reacting at 95-100°C and 400-500 r / min for 6-7 h, washing with pure water at 70-80°C for 3-4 times, and vacuum drying at 50-60°C for 10-12 h.

[0034] As an optimization, the reaction process of the phosphoric acid-modified monomer in step (5) is as follows:

[0035] .

[0036] As an optimization, the anionic polymer in step (6) is prepared by uniformly mixing 5-6 parts of acrylamide, 2.8-3.36 parts of phosphoric acid-modified monomer, 1.08-1.29 parts of maleic anhydride, 2.28-2.73 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 16-20 parts of pure water, and then cooling the mixture to 7°C under a nitrogen atmosphere at 400-500 r / min. A composite initiator prepared by uniformly mixing 0.05-0.06 parts of ammonium persulfate, 0.02-0.022 parts of ascorbic acid, 0.01-0.012 parts of azobisisobutyramidine hydrochloride, and 0.05-0.06 parts of azobisisobutyronitrile is added, and the mixture is reacted for 2.5-3 hours, cooled to room temperature, taken out, cut into pieces, vacuum-dried at 60-70°C for 3-4 hours, and granulated after crushing.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] In the preparation of the anti-scaling cross-linked polymer fracturing fluid, the present invention comprises the following steps: firstly reacting allylamine hydrochloride with epichlorohydrin to obtain a double-bond chlorinated intermediate; reacting the double-bond chlorinated intermediate with laurylamidopropyl dimethylamine to obtain a cationic monomer; copolymerizing the cationic monomer with acrylamide via a composite initiator to obtain a cationic polymer; reacting L-lysine with formaldehyde and phosphorous acid to obtain phosphoric acid-modified lysine; reacting the phosphoric acid-modified lysine with allyl glycidyl ether to obtain a phosphoric acid-modified monomer; copolymerizing acrylamide with the phosphoric acid-modified monomer, maleic anhydride and 2-acrylamido-2-methylpropanesulfonic acid via a composite initiator to obtain an anionic polymer; and dissolving the anionic polymer and the cationic polymer in water to prepare the anti-scaling cross-linked polymer fracturing fluid.

[0039] First, allylamine hydrochloride releases active amino groups under the alkaline conditions of triethylamine, allowing the amino groups to react with epoxy groups, thereby preparing a double-bond chlorinated intermediate with a double bond and a chlorinated hydrocarbon; the chlorine atom on the double-bond chlorinated intermediate undergoes a quaternization reaction with the tertiary amine group on laurylamidopropyldimethylamine, thereby obtaining a cationic monomer with a double positive charge, and the long-chain alkane carried by the monomer can effectively improve the lipophilicity, viscosity-enhancing effect and heat resistance; the cationic monomer with a double bond and acrylamide undergo a copolymerization reaction under the action of a composite initiator, and the composite initiator simultaneously introduces a redox initiation system and a free radical initiation system, which can make the cationic polymer obtained by polymerization have a more stable molecular weight, as well as better viscosity-enhancing effect, heat resistance and shear resistance.

[0040] Secondly, L-lysine is modified by the Mannich reaction, and a large number of phosphate groups are introduced into the amino groups thereon. The phosphate group is a negatively charged group and can prevent the formation of scale deposits through chelation, lattice distortion and other pathways. The epoxy group on allyl glycidyl ether reacts with the carboxyl group on the phosphate-modified lysine to introduce a double bond group to obtain a phosphate-modified monomer. Subsequently, under the initiation action of a composite initiator, acrylamide, the phosphate-modified monomer, maleic anhydride, and 2-acrylamido-2-methylpropanesulfonic acid undergo copolymerization to obtain an anionic polymer. The anionic polymer has a large number of negatively charged groups, such as phosphate groups, carboxyl groups, and sulfonic acid groups. These anionic groups have different scale inhibition effects on different scale deposits. After copolymerizing these monomers together, through their synergistic effect, they can achieve effective scale prevention for most scale deposits and effectively prevent scale deposits from invading pipelines. At the same time, the use of a composite initiator can make the anionic polymer obtained by polymerization have a more stable molecular weight, as well as better viscosity-increasing effect, temperature resistance, and shear resistance.

[0041] Finally, the anionic polymer and the cationic polymer are mixed and dissolved in water to form an anti-scaling cross-linked polymer fracturing liquid. The negatively charged groups on the anionic polymer and the positively charged groups on the cationic polymer self-associate through electrostatic binding, achieving the effect of cross-linking and thickening, avoiding the risk of contaminating the bottom layer caused by the use of organic metal cross-linking agents, and the gel is broken thoroughly with little residue, which has a good fracturing construction effect. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] In all the following examples and comparative examples, sodium formate was used as the anti-crosslinking agent.

[0044] Example 1:

[0045] A method for preparing a scale-resistant cross-linked polymer fracturing fluid, comprising the following steps:

[0046] (1) 4 parts of allylamine hydrochloride, 4.76 parts of triethylamine, and 40 parts of methanol were mixed uniformly by mass. 8.9 parts of epichlorohydrin were added dropwise in an ice-water bath within 1 hour. After the addition was completed, the mixture was reacted at 25°C and 300 r / min for 15 hours. The mixture was filtered and the solvent was removed by rotary evaporation to obtain a double-bond chlorinated intermediate.

[0047] (2) By weight, 4 parts of double-bond chlorinated intermediate, 11.75 parts of lauryl amide propyl dimethylamine, and 15 parts of anhydrous ethanol were mixed evenly, refluxed at 80°C for 24 hours, and the solvent was removed by rotary evaporation. The mixture was washed three times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate was rotary evaporated to obtain a cationic monomer;

[0048] (3) By weight, 5 parts of acrylamide, 6.34 parts of cationic monomer, 30 parts of pure water, and 0.3 parts of sodium formate were mixed evenly. Under a nitrogen atmosphere, 45°C, 400 r / min, a composite initiator prepared by mixing 0.025 parts of ammonium persulfate, 0.01 parts of ascorbic acid, 0.005 parts of azobisisobutylamidine hydrochloride, and 0.025 parts of azobisisobutylonitrile was added. The mixture was reacted for 2 h, cooled to room temperature, washed twice with anhydrous ethanol, filtered, and the solid was vacuum dried at 60°C for 6 h. After crushing and granulation, a cationic polymer was obtained.

[0049] (4) By weight, 6 parts of L-lysine, 20 parts of 40 wt% formaldehyde aqueous solution, and 13.46 parts of phosphorous acid were mixed uniformly, refluxed at 105°C for 3 h, and dried at 50°C for 12 h to obtain phosphoric acid-modified lysine;

[0050] (5) By weight, 5 parts of phosphoric acid-modified lysine, 1.09 parts of allyl glycidyl ether, and 0.006 parts of hexadecyltrimethylammonium bromide were mixed evenly, stirred at 60°C, 300 r / min for 30 min, reacted at 95°C, 400 r / min for 7 h, washed with 70°C pure water 4 times, and vacuum dried at 50°C for 12 h to obtain a phosphoric acid-modified monomer;

[0051] (6) By weight, 5 parts of acrylamide, 2.8 parts of phosphoric acid-modified monomer, 1.08 parts of maleic anhydride, 2.28 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 16 parts of pure water were mixed evenly, cooled to 7°C under a nitrogen atmosphere, and a composite initiator prepared by mixing 0.05 parts of ammonium persulfate, 0.02 parts of ascorbic acid, 0.01 parts of azobisisobutyramidine hydrochloride, and 0.05 parts of azobisisobutyronitrile was added. The mixture was reacted for 3 hours, cooled to room temperature, taken out, cut into pieces, and vacuum-dried at 60°C for 4 hours. After crushing, the mixture was granulated to obtain an anionic polymer.

[0052] (7) 5 parts of cationic polymer, 2 parts of anionic polymer and 1000 parts of pure water were mixed uniformly by mass and stirred at 200 r / min for 40 min at room temperature to prepare anti-scaling cross-linked polymer fracturing fluid.

[0053] Example 2:

[0054] A method for preparing a scale-resistant cross-linked polymer fracturing fluid, comprising the following steps:

[0055] (1) By weight, 4.5 parts of allylamine hydrochloride, 5.35 parts of triethylamine, and 45 parts of methanol were mixed evenly. In an ice-water bath, 10.01 parts of epichlorohydrin were added dropwise within 1 hour. After the addition was completed, the mixture was reacted at 28°C and 350 r / min for 14.5 hours. The mixture was filtered and the solvent was removed by rotary evaporation to obtain a double-bond chlorinated intermediate.

[0056] (2) By weight, 4.5 parts of double-bond chlorinated intermediate, 13.22 parts of lauryl amide propyl dimethylamine, and 18 parts of anhydrous ethanol were mixed evenly, refluxed at 82°C for 23 hours, and the solvent was removed by rotary evaporation. The mixture was washed three times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate was rotary evaporated to obtain a cationic monomer;

[0057] (3) By weight, 5.5 parts of acrylamide, 6.97 parts of cationic monomer, 32 parts of pure water, and 0.35 parts of sodium formate were mixed evenly. Under a nitrogen atmosphere, at 48°C and 450 r / min, a composite initiator prepared by mixing 0.028 parts of ammonium persulfate, 0.0105 parts of ascorbic acid, 0.0055 parts of azobisisobutyramidine hydrochloride, and 0.028 parts of azobisisobutyronitrile was added. The mixture was reacted for 2 h, cooled to room temperature, washed twice with anhydrous ethanol, filtered, and the solid was vacuum dried at 65°C for 5.5 h. After crushing and granulation, a cationic polymer was obtained.

[0058] (4) By weight, 6.5 parts of L-lysine, 22 parts of 40 wt% formaldehyde aqueous solution, and 14.58 parts of phosphorous acid were mixed uniformly, refluxed at 108°C for 2.8 h, and dried at 55°C for 11 h to obtain phosphoric acid-modified lysine;

[0059] (5) By weight, 5.5 parts of phosphoric acid-modified lysine, 1.2 parts of allyl glycidyl ether, and 0.0065 parts of hexadecyltrimethylammonium bromide were mixed evenly, stirred at 62°C, 350 r / min for 25 min, reacted at 98°C, 450 r / min for 6.5 h, washed three times with pure water at 75°C, and vacuum dried at 55°C for 11 h to obtain a phosphoric acid-modified monomer;

[0060] (6) By weight, 5.5 parts of acrylamide, 3.08 parts of phosphoric acid-modified monomer, 1.19 parts of maleic anhydride, 2.51 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 18 parts of pure water were mixed evenly, cooled to 7°C under a nitrogen atmosphere, and spun at 450 r / min. A composite initiator prepared by mixing 0.055 parts of ammonium persulfate, 0.021 parts of ascorbic acid, 0.011 parts of azobisisobutyramidine hydrochloride, and 0.055 parts of azobisisobutyronitrile was added. The mixture was reacted for 2.8 hours, cooled to room temperature, taken out, cut into pieces, and vacuum-dried at 65°C for 3.5 hours. The mixture was crushed and granulated to obtain an anionic polymer.

[0061] (7) 5.5 parts of cationic polymer, 2.5 parts of anionic polymer and 1000 parts of pure water were mixed uniformly by weight, and stirred at 250 r / min for 35 min at room temperature to prepare an anti-scaling cross-linked polymer fracturing fluid.

[0062] Example 3:

[0063] A method for preparing a scale-resistant cross-linked polymer fracturing fluid, comprising the following steps:

[0064] (1) 5 parts of allylamine hydrochloride, 5.95 parts of triethylamine, and 50 parts of methanol were mixed uniformly by mass. 11.13 parts of epichlorohydrin were added dropwise in an ice-water bath over 1 hour. After the addition was complete, the mixture was reacted at 30°C and 400 rpm for 14 hours. The mixture was filtered and the solvent was removed by rotary evaporation to obtain a double-bond chlorinated intermediate.

[0065] (2) By weight, 5 parts of double-bond chlorinated intermediate, 14.69 parts of lauryl amide propyl dimethylamine, and 20 parts of anhydrous ethanol were mixed evenly, refluxed at 85°C for 24 hours, and the solvent was removed by rotary evaporation. The mixture was washed four times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate was rotary evaporated to obtain a cationic monomer;

[0066] (3) By weight, 6 parts of acrylamide, 7.61 parts of cationic monomer, 35 parts of pure water, and 0.4 parts of sodium formate were mixed uniformly. Under a nitrogen atmosphere, 50°C, 500 r / min, a composite initiator prepared by mixing 0.03 parts of ammonium persulfate, 0.011 parts of ascorbic acid, 0.006 parts of azobisisobutylamidine hydrochloride, and 0.03 parts of azobisisobutylonitrile was added. The mixture was reacted for 2 h, cooled to room temperature, washed with anhydrous ethanol three times, filtered, and the solid was vacuum dried at 70°C for 5 h. After crushing and granulation, a cationic polymer was obtained.

[0067] (4) By weight, 7 parts of L-lysine, 24 parts of 40 wt% formaldehyde aqueous solution, and 15.71 parts of phosphorous acid were mixed uniformly, refluxed at 110°C for 2.5 h, and dried at 60°C for 10 h to obtain phosphoric acid-modified lysine;

[0068] (5) By weight, 6 parts of phosphoric acid-modified lysine, 1.31 parts of allyl glycidyl ether, and 0.007 parts of hexadecyltrimethylammonium bromide were mixed evenly, stirred at 65°C, 400 r / min for 30 min, reacted at 100°C, 500 r / min for 6 h, washed three times with 80°C pure water, and vacuum dried at 60°C for 10 h to obtain a phosphoric acid-modified monomer;

[0069] (6) By weight, 6 parts of acrylamide, 3.36 parts of phosphoric acid-modified monomer, 1.29 parts of maleic anhydride, 2.73 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 20 parts of pure water were mixed evenly, cooled to 7°C under a nitrogen atmosphere, and a composite initiator prepared by mixing 0.06 parts of ammonium persulfate, 0.022 parts of ascorbic acid, 0.012 parts of azobisisobutyramidine hydrochloride, and 0.06 parts of azobisisobutyronitrile was added. The mixture was reacted for 2.5 hours, cooled to room temperature, taken out, cut into pieces, and vacuum-dried at 70°C for 3 hours. After crushing, the mixture was granulated to obtain an anionic polymer.

[0070] (7) 6 parts of cationic polymer, 3 parts of anionic polymer and 1000 parts of pure water were mixed uniformly by mass and stirred at 300 r / min for 30 min at room temperature to prepare anti-scaling cross-linked polymer fracturing fluid.

[0071] Comparative Example 1:

[0072] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 1 differs from that of Example 2 in that step (2) is modified as follows: 4.5 parts by mass of a double-bond chlorinated intermediate, 4.7 parts by mass of N,N-dimethylbutylamine, and 18 parts by mass of anhydrous ethanol are uniformly mixed, refluxed at 82° C. for 23 h, and the solvent is removed by rotary evaporation. The mixture is washed three times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate is rotary evaporated to obtain a cationic monomer. The remaining steps are the same as those of Example 2.

[0073] Comparative Example 2:

[0074] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 2 differs from that of Example 2 in step (3). Step (3) is modified as follows: 5.5 parts of acrylamide, 6.97 parts of cationic monomer, 32 parts of pure water, and 0.35 parts of sodium formate are uniformly mixed, and 0.05 parts of azobisisobutyronitrile are added under a nitrogen atmosphere at 60°C and 450 r / min. The mixture is reacted for 2 hours, cooled to room temperature, washed twice with anhydrous ethanol, filtered, and the solid is vacuum dried at 65°C for 5.5 hours. The solid is crushed and granulated to obtain a cationic polymer. The remaining steps are the same as those of Example 2.

[0075] Comparative Example 3:

[0076] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 3 differs from that of Example 2 in that steps (1), (2), and (3) are omitted, and step (7) is modified as follows: 2.5 parts by mass of anionic polymer and 1000 parts by mass of pure water are uniformly mixed, and stirred at 250 rpm for 35 minutes at room temperature to prepare the anti-scaling cross-linked polymer fracturing fluid. The remaining steps are the same as those of Example 2.

[0077] Comparative Example 4:

[0078] The preparation method of the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 4 is different from that of Example 2 in that step (4) is not performed, and step (5) is modified as follows: 5.5 parts of L-lysine, 4.3 parts of allyl glycidyl ether, and 0.0065 parts of hexadecyltrimethylammonium bromide are mixed uniformly by mass, first stirred at 62°C and 350r / min for 25min, reacted at 98°C and 450r / min for 6.5h, washed with pure water at 75°C for 3 times, and vacuum dried at 55°C for 11h to obtain a modified lysine monomer; step (6 ... 5.5 parts of acrylamide, 3.08 parts of modified lysine monomer, 1.19 parts of maleic anhydride, 2.51 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 18 parts of pure water were mixed uniformly. The mixture was cooled to 7°C under a nitrogen atmosphere and spun at 450 rpm. A composite initiator prepared by uniformly mixing 0.055 parts of ammonium persulfate, 0.021 parts of ascorbic acid, 0.011 parts of azobisisobutylamidine hydrochloride, and 0.055 parts of azobisisobutylonitrile was added. The mixture was allowed to react for 2.8 hours. The mixture was cooled to room temperature, removed, cut into pieces, vacuum-dried at 65°C for 3.5 hours, crushed, and granulated to produce an anionic polymer. The remaining steps were the same as in Example 2.

[0079] Comparative Example 5:

[0080] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 5 differs from that of Example 2 in that step (6) is modified as follows: 5.5 parts of acrylamide, 1.19 parts of maleic anhydride, 2.51 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 18 parts of pure water are mixed uniformly by mass, cooled to 7°C under a nitrogen atmosphere, and a composite initiator prepared by mixing 0.055 parts of ammonium persulfate, 0.021 parts of ascorbic acid, 0.011 parts of azobisisobutylamidine hydrochloride, and 0.055 parts of azobisisobutylonitrile is added. The mixture is reacted for 2.8 hours, cooled to room temperature, removed, cut into pieces, vacuum dried at 65°C for 3.5 hours, crushed, and granulated to obtain an anionic polymer. The remaining steps are the same as those of Example 2.

[0081] Comparative Example 6:

[0082] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 6 differs from that of Example 2 in that step (6) is modified as follows: 5.5 parts of acrylamide, 3.08 parts of phosphoric acid-modified monomer, 2.51 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 18 parts of pure water are mixed uniformly by mass, cooled to 7°C under a nitrogen atmosphere, and spun at 450 r / min. A composite initiator prepared by mixing 0.055 parts of ammonium persulfate, 0.021 parts of ascorbic acid, 0.011 parts of azobisisobutylamidine hydrochloride, and 0.055 parts of azobisisobutylonitrile is added. The mixture is reacted for 2.8 hours, cooled to room temperature, removed, cut into pieces, vacuum-dried at 65°C for 3.5 hours, crushed, and granulated to obtain an anionic polymer. The remaining steps are the same as those of Example 2.

[0083] Comparative Example 7:

[0084] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 7 differs from that of Example 2 in that step (6) is modified as follows: 5.5 parts of acrylamide, 3.08 parts of phosphoric acid-modified monomer, 1.19 parts of maleic anhydride, and 18 parts of pure water are mixed uniformly by mass, cooled to 7°C under a nitrogen atmosphere, and spun at 450 r / min. A composite initiator prepared by mixing 0.055 parts of ammonium persulfate, 0.021 parts of ascorbic acid, 0.011 parts of azobisisobutylamidine hydrochloride, and 0.055 parts of azobisisobutylonitrile is added. The mixture is reacted for 2.8 hours, cooled to room temperature, removed, cut into pieces, vacuum-dried at 65°C for 3.5 hours, crushed, and granulated to obtain an anionic polymer. The remaining steps are the same as those of Example 2.

[0085] Comparative Example 8:

[0086] The method for preparing the anti-scaling cross-linked polymer fracturing fluid of Comparative Example 8 differs from that of Example 2 in that step (6) is modified as follows: 5.5 parts of acrylamide, 3.08 parts of phosphoric acid-modified monomer, 1.19 parts of maleic anhydride, 2.51 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 18 parts of pure water are mixed uniformly by mass, cooled to 7°C under a nitrogen atmosphere, and spun at 450 rpm. An initiator prepared by mixing 0.075 parts of ammonium persulfate and 0.032 parts of ascorbic acid is added, reacted for 2.8 hours, cooled to room temperature, removed, cut into pieces, vacuum dried at 65°C for 3.5 hours, crushed, and granulated to obtain an anionic polymer. The remaining steps are the same as those of Example 2.

[0087] Test Example 1:

[0088] Viscosity, temperature resistance and shear resistance test: The apparent viscosity, temperature resistance and shear viscosity of the prepared anti-scaling cross-linked polymer fracturing fluid are tested to evaluate its temperature resistance and temperature resistance and shear resistance. The specific test methods are as follows:

[0089] Apparent viscosity: 500 ml of the prepared anti-scaling cross-linked polymer fracturing fluid was taken into a beaker and measured using a ZNND six-speed rotational viscometer at room temperature and a shear rate of 170 s -1 The apparent viscosity under the test conditions was tested 5 times in parallel for each group of samples, and the average value was recorded;

[0090] Temperature resistance: With reference to the standard SY / T 5107-2005, the prepared anti-scaling cross-linked polymer fracturing fluid was tested using a HAAKE MARS III high temperature and high pressure rheometer at a shear rate of 170s -1 The temperature resistance temperature corresponding to the viscosity dropping to 50mPa·s was measured. Each group of samples was tested 5 times in parallel and the average value was recorded.

[0091] Temperature and shear resistance: With reference to the standard SY / T 5107-2005, the prepared anti-scaling cross-linked polymer fracturing fluid was tested using a HAAKE MARS III high temperature and high pressure rheometer at 100°C and a shear rate of 170s -1 , shear viscosity after shearing for 1 hour, each group of samples was tested in parallel 5 times, and the average value was recorded.

[0092] The results are shown in Table 1.

[0093] Table 1

[0094] Apparent viscosity / mPa·s Temperature resistance / ℃ Shear viscosity / mPa·s Example 1 274.1 145.7 127.4 Example 2 281.5 146.9 132.7 Example 3 289.3 148.3 135.2 Comparative Example 1 254.2 134.2 115.3 Comparative Example 2 248.4 126.8 109.6 Comparative Example 3 34.5 / 15.4 Comparative Example 4 241.3 134.8 118.4 Comparative Example 5 232.6 132.5 113.8 Comparative Example 6 259.3 138.6 123.5 Comparative Example 7 254.2 136.5 119.1 Comparative Example 8 247.8 131.2 112.3

[0095] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 8 in Table 1, it can be found that the anti-scaling cross-linked polymer fracturing fluid prepared by the present invention has good viscosity increasing effect, temperature resistance and heat and shear resistance.

[0096] By comparing the data in the table, the data of Comparative Example 1 shows that the long carbon chain on the cationic monomer effectively improves the viscosity-increasing effect, temperature resistance and heat resistance and shear resistance; the data of Comparative Example 2 shows that the introduction of the composite initiator system effectively improves the molecular chain shape of the cationic polymer, making its molecular weight more stable, and having better viscosity-increasing effect, temperature resistance and heat resistance and shear resistance; the data of Comparative Example 3 shows that the cationic polymer and the anionic polymer produce self-association. In the case of no cationic polymer, the only anionic polymer cannot be cross-linked, and thus a fracturing fluid that meets the viscosity standard cannot be obtained; the data of Comparative Examples 4 and 5 show that the phosphoric acid modification of lysine provides More electrostatic binding sites are obtained, thereby obtaining a better cross-linking effect, improving the viscosity-increasing effect, temperature resistance and heat resistance and shear resistance; the data of Comparative Examples 6 and 7 show that the addition of maleic anhydride and 2-acrylamido-2-methylpropanesulfonic acid monomers enables the anionic copolymer to have a better viscosity-increasing effect, and also improves the temperature resistance and heat resistance and shear resistance; the data of Comparative Example 8 shows that the use of the composite initiator system in the copolymerization process of the anionic polymer effectively improves the molecular chain structure, molecular weight and molecular weight distribution of the anionic polymer, and effectively improves the viscosity, temperature resistance and heat resistance and shear resistance of the compounded anti-scaling cross-linked polymer fracturing fluid.

[0097] Test Example 2:

[0098] Anti-scaling performance test: The scale inhibition efficiency of the prepared anti-scaling cross-linked polymer fracturing fluid against calcium carbonate scale, calcium sulfate scale, and barium sulfate scale was tested with reference to standard Q / SY 17126-2019. Each group of samples was tested in parallel 5 times, and the average value was recorded.

[0099] The results are shown in Table 2.

[0100] Table 2

[0101] Calcium carbonate scale inhibition rate Calcium sulfate scale inhibition rate Barium sulfate scale inhibition rate Example 1 99.18% 98.78% 97.48% Example 2 99.25% 98.89% 97.55% Example 3 99.04% 98.72% 97.42% Comparative Example 1 99.01% 98.80% 97.49% Comparative Example 2 99.11% 98.83% 97.51% Comparative Example 3 99.03% 98.79% 97.47% Comparative Example 4 85.49% 91.56% 86.24% Comparative Example 5 80.44% 88.64% 81.15% Comparative Example 6 89.27% 83.22% 92.33% Comparative Example 7 86.44% 94.65% 88.48% Comparative Example 8 99.08% 98.76% 97.40%

[0102] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 8 in Table 2, it can be found that the anti-scaling cross-linked polymer fracturing fluid prepared in the present invention has good anti-scaling performance.

[0103] By comparing the data in the table, the data of Comparative Example 4 shows that lysine that has not been modified with phosphoric acid can also provide some anti-scaling performance because it still has a carboxyl group. At the same time, the epoxy group no longer reacts with the carboxyl group, but reacts with the unreacted amino group, thereby vacating the carboxyl group. It also shows that the introduction of a large number of phosphoric acid groups brings about good anti-scaling performance; the data of Comparative Example 5 shows that the introduced phosphoric acid groups have good anti-scaling performance; the data of Comparative Example 6 shows that the introduction of maleic anhydride improves the anti-scaling performance, especially the anti-scaling performance against calcium sulfate; the data of Comparative Example 7 shows that the introduction of sulfonic acid groups also partially improves the anti-scaling performance.

[0104] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a scale-resistant cross-linked polymer fracturing fluid, characterized in that: The method comprises the following preparation steps: (1) By weight, 4-5 parts of allylamine hydrochloride, 4.76-5.95 parts of triethylamine, and 40-50 parts of methanol were mixed evenly. In an ice-water bath, 8.9-11.13 parts of epichlorohydrin were added dropwise within 1 hour. After the addition was completed, the mixture was reacted at 25-30°C and 300-400 r / min for 14-15 hours. The mixture was filtered and the solvent was removed by rotary evaporation to obtain a double-bond chlorinated intermediate. (2) By weight, 4 to 5 parts of the double-bond chlorinated intermediate, 11.75 to 14.69 parts of lauryl amide propyl dimethylamine, and 15 to 20 parts of anhydrous ethanol were mixed evenly, refluxed at 80 to 85°C for 22 to 24 hours, and the solvent was removed by rotary evaporation. The mixture was washed 3 to 4 times with a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:15, filtered, and the filtrate was rotary evaporated to obtain a cationic monomer; (3) acrylamide, cationic monomer, pure water, and anti-crosslinking agent are mixed, and a composite initiator prepared by uniformly mixing ammonium persulfate, ascorbic acid, azobisisobutylamidine hydrochloride, and azobisisobutylonitrile is added under a nitrogen atmosphere, and the mixture is reacted, cooled, washed, filtered, dried, crushed, and granulated to obtain a cationic polymer; (4) By weight, 6-7 parts of L-lysine, 20-24 parts of 40 wt% formaldehyde aqueous solution, and 13.46-15.71 parts of phosphorous acid were mixed uniformly, refluxed at 105-110°C for 2.5-3 hours, and dried at 50-60°C for 10-12 hours to obtain phosphoric acid-modified lysine; (5) By weight, 5-6 parts of phosphoric acid-modified lysine, 1.09-1.31 parts of allyl glycidyl ether, and 0.006-0.007 parts of hexadecyltrimethylammonium bromide were mixed evenly, first stirred at 60-65°C and 300-400 r / min for 20-30 min, reacted at 95-100°C and 400-500 r / min for 6-7 h, washed with pure water at 70-80°C for 3-4 times, and vacuum dried at 50-60°C for 10-12 h to obtain a phosphoric acid-modified monomer; (6) acrylamide, phosphoric acid-modified monomer, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid, and pure water are mixed, cooled under a nitrogen atmosphere, and a composite initiator prepared by uniformly mixing ammonium persulfate, ascorbic acid, azobisisobutylamidine hydrochloride, and azobisisobutylonitrile is added, reacted, cooled, taken out, cut into pieces, dried, crushed, and granulated to obtain an anionic polymer; (7) By weight, 5-6 parts of cationic polymer, 2-3 parts of anionic polymer, and 1000 parts of pure water were mixed evenly, and stirred at 200-300 r / min for 30-40 min at room temperature to prepare an anti-scaling cross-linked polymer fracturing fluid; The anti-crosslinking agent in step (3) is one of sodium formate and urea.

2. The method for preparing a scale-resistant cross-linked polymer fracturing fluid according to claim 1, characterized in that: The cationic polymer in step (3) is prepared by uniformly mixing 5 to 6 parts of acrylamide, 6.34 to 7.61 parts of cationic monomer, 30 to 35 parts of pure water and 0.3 to 0.4 parts of anti-crosslinking agent in parts by mass, adding a composite initiator prepared by uniformly mixing 0.025 to 0.03 parts of ammonium persulfate, 0.01 to 0.011 parts of ascorbic acid, 0.005 to 0.006 parts of azobisisobutylamidine hydrochloride and 0.025 to 0.03 parts of azobisisobutylonitrile under a nitrogen atmosphere at 45 to 50°C and 400 to 500 r / min, reacting for 2 hours, cooling to room temperature, washing with anhydrous ethanol for 2 to 3 times, filtering, and drying the solid in a vacuum at 60 to 70°C for 5 to 6 hours, crushing and granulating to obtain the product.

3. The method for preparing a scale-resistant cross-linked polymer fracturing fluid according to claim 1, characterized in that: The anionic polymer in step (6) is prepared by uniformly mixing 5 to 6 parts of acrylamide, 2.8 to 3.36 parts of phosphoric acid-modified monomer, 1.08 to 1.29 parts of maleic anhydride, 2.28 to 2.73 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 16 to 20 parts of pure water, and then cooling the mixture to 7°C under a nitrogen atmosphere at 400 to 500 r / min. A composite initiator prepared by uniformly mixing 0.05 to 0.06 parts of ammonium persulfate, 0.02 to 0.022 parts of ascorbic acid, 0.01 to 0.012 parts of azobisisobutyramidine hydrochloride, and 0.05 to 0.06 parts of azobisisobutyronitrile is added, and the mixture is reacted for 2.5 to 3 hours, cooled to room temperature, taken out, cut into pieces, vacuum-dried at 60 to 70°C for 3 to 4 hours, crushed, and granulated to obtain the obtained product.

4. An anti-scaling cross-linked polymer fracturing fluid prepared according to the method for preparing an anti-scaling cross-linked polymer fracturing fluid according to any one of claims 1 to 3.